1. Field of the Invention
This invention relates to a lubrication system for a power take off assembly and a drive shaft therefor and, more specifically, to such a lubrication system which will operate independently of the coupling or uncoupling of a power take off assembly.
2. Description of the Prior Art
There are a number of multi-drive vehicles which utilize a main transmission and a transfer case which is capable of providing power to the rear axle alone or to both the front and rear axles at the same time. Typical transfer cases of this type are disclosed in U.S. Pat. Nos. 3,095,758; 3,557,634 and 3,679,016.
It is not uncommon in transfer cases to include a means for providing a multi-speed power transmission function in the form of high and low speed operations. Transfer cases such as those disclosed in U.S. Pat. Nos. 3,941,199 and 4,188,838 include such features and significantly increase the selective operating gear ratios which are available to the operator of a vehicle which uses a main transmission in conjunction with the transfer case.
However, in transmission devices of this type lubrication is often provided by the splashing of lubricating oil around the interior of the housing. The oil may be caught in channels or trays to be supplied to specific shaft bearing by gravity flow. However, in some configurations, where gears or other elements may be mounted for relative rotation on shafts which, in turn, rotate, the ineffectiveness of splash or gravity lubrication becomes apparent because of the many restricted locations needing lubricating oil. If the shafts are mounted in an upper region of the transmission device housing remote from the oil pump, the reliability of this type of lubrication system is further reduced.
To alleviate some of these problems, a Pressurized Lubrication System as disclosed in U.S. Patent Application Ser. No. 165,800 filed by Joseph L. Malkowski and Calvin G. Wells on Aug. 3, 1980 and issued on Jan. 18, 1983 as U.S. Pat. No. 4,368,802 has been introduced to provide lubricating oil to a plurality of elements mounted on the rotatable shaft of a transfer case. For this pressurized system to properly operate, the oil pump was mounted at the end of the shaft to be directly driven thereby. However, it is sometimes desirable to include a power take off assembly for the transfer case which can be mounted directly to the housing in alignment with the input shaft which specifically needs this type of pressurized lubrication system. Additionally, the power take off assembly needs lubrication for the rotating elements mounted herein and the splash or gravity types of lubrication systems mentioned hereinabove have been found to be generally unsatisfactory because the power take off assemblies are generally mounted on the housing in a region thereof remote from the oil sump.